Arrangement for controlling volume range



Dec. 15 1925- A. B. CLARK ARRANGEMENT FOR CONTROLLING VOLUME RANGE Filed June 19. 1924 INVENTOR J19. 6/0/40 B Y f qg A'TTOL ENE Y ALVA"- Patented Dec. 15, 1925.

' i ,Tl ventiong 'elatesto transmission ciri its,

finorf 1 particularly fjto arrange; ments iorlenabl mg a transm ssion medium inherentlyicepable of ,tr&ns,n1itting only a n w volumetto produ e t.

receiving "stat ons wider rengefof valuat on 111 volume than the medium. 1s, able toitr' ansl 15: M V

In tliefeeseof a transmission medium'i 'such "as (an ordinary t"elep h.one line, the

range of volume yeriaition of the trans- 'mitted' signal is limited by factors which" ai'enot' under control; Intra nsmitting high Q grade performiinces',

' selectionsjthe range o I V is frequently quite large. In orderto' t'ransf init suchmateriel o vena' medium. of limited ,yolu'me range, it will .be necessary tof ,niQdi- 'f yl e v y i d 1 ve y o pa' sages, "bothf'to bringthem the limits im posed by flthe m diunipfwith it consequent."

"1 loss infjthe 'contrest between the, piano and 1 w p,

5 "it" is proposed "to overcome this dif lie ulty" w e ar y ivm eml. Variation n, olume 'forteparts' by regulating the volume impressed upon "1 thetrzfinsmission medium'et-jthe transmit-.

36' station so as to keep it Withinthelimits of 'inedium, and et the same time =pro- (lucing a change in some" transmission e 1ement at the receiving station tofcom'pensate" flier the change imavdefz t th'e "transmittingstation. iFor' exampleiijif thefi 'olume reduced bef ore being 'i1npres'sed guponf thej transmitting medium, a tr nsmission 'eIe-Q ment et the receiving statioh'willfibe ad; 7 v jus'ted so a's'to eorrespondingly increase the volume, a nd Vioe verfsa.

f This method is useful partieiilarlji"conj ,nec tion with: public [address andfllredio is limited. g

,ibroadcisting systems where ajipro m deliveredfgit one point must be transmitted to an; audience located it e distant 'p'ointl oyer medium v hose"'vol u'me. range a a transmission 1 understqocl from. the follloivingideteil ed denemmx; or Bnoox'mzm NEW Yonm hssmnon T0; AME RIM nu) mnmennrnw com-21mm n conronn'rron or NEWPYOBK v .M j I which the" f Inecc ordan'ce with the p'resent invention' The invent on now be imore r'v'ith the accompanying"drawing; igure 1 "of which shows ,2 circ'uifi' arrangeinentj embodying thefprinciples of the invention; [end Fig32 of which is: 'a transmission 1e gram 'illu'streting the 1 operation of 'cuitlof Fig. 1; Q? i 1 Referring to Fig. 1, L indicates a telehone transmission line extending from staion A to; station B.' "The line "L 1s rovided r16 4 also-called pickup microphone M is provided for picking up'ithefmusical selecstation B. An amplifier, or repeater R is rogram: transmitted I overdthe' line tov an audience. -w, t. E

In order "to keep the volume impressed 'up on th'e linelL from the repeater R withinjthe, yolum'e limits 'of the transmission "circuit, a volum'e' 'regulating arrangement is 'prorided which? com rises an emplifying vac'uum'tube' 10 having an'ad'ustable p0- tien'tiometer ll in its input circuit. By suitable-"adjustment of, the potentiometer 11, the'potentia1 ap lied to the gridmay be adju'sted so that t e output fromthe tube 10 ay be made either greater or less than the input. If thejf volumedeliVe-red by the repieatelffli is. reater than the maximum lim- 'itiof which the 1ine L is capable, thepotentiome'ter 11 will be aldjusted so that the Vacuum gftribe I v10 will reduce the amplitude before .itis im r'esseicl on the line.- If, on thew ot'h erjhan the volume delivered by the frepeaterR'. smaller thanthe minimum carry withoutjproducing undesirable effects atlthe receiving station, the "potentiometer 11will beed'ustedfsoes to causethe tube 110 to ampli the currents and impress them upon the; line L' with 'a volumefsufi'b cie'n tly great} 'for proper. transmission.

The limiting fec tors w'hich determine the mfaximuniend minimum Volumes which the line "will properly transmit: are usually the ioverloedingj of the vacuum l tubes of the rei 'peaters 'on' the one hand, and the a'mbuntof "with. amplifiers or" re eaters of a we l known typei as'mdicatedet B andB "At sta Volume which the transmission line L wiu' .tion' or other program 'to be transmitted to v t j ti nith f, wh n re a d i'n. connection noise present in the" transmission circuit on 9 the other hand. That is to say, the maxi-. mum volume of the circuit is limited by the power carrying capacity of the repeaters and'by the fact that the power must not be allowed to become so strong that it w ll produce serious crosstalk in the other circuits. The minimum value is limited by the amount of noise present in the transmission circuit due to various causes, such as paralleling power lines and paralleling telephone and telegraph circuits. In the case of rad o transmission circuits, the range of volume 18 similarly limited bythe power transmitting capacity of the wireless station on the one hand, and the noise due to static and other causes on'the other. hand.

The regulation of volume above described of course results in the transmission of Suecessive passages of a musical selection, for

ing of a vacuum tube 12 having associated therewith a potentiometer 13. By suitably adjusting the potentiometer 13, the vacuum tube 12 may be caused to deliver more or less power than is applied to its input circuit. It will be seen, therefore, that if, when the volume supplied by the repeater R exceeds the maximum to be transmitted over the line L so that the potentiometer 11 is adjusted to reduce the volume, the transmission' arriving at the receiving station may be brought back to its proper comparative volume by adjusting the potentiometer 13 to cause the tube 12 to amplify the currents.

Likewise, if the potentiometer 11 is adjusted to increase the volume, the potentiometer 13 may be adjusted to decrease the volume.

In order that the adjustment of the volumecontrolling arrangement at the station B may be controlled by the volume adjustment made at station A, an auxiliary circuit 'L is provided, said auxiliary circuit having repeaters R',, R, and Bi as in the case of the circuit L. At the transmitting enda generator of some suitable frequency G is "provided, and at the receiving end a magnetic arrangement 14 is connected to the circuit L. The magnetic arrangement is responsive to alternating current. and depending upon the amplitude of the alternating current received, will attract its core 15 more or less, thereby causing a corresponding adjustment of the potentiometer 13. At the station A an adjustable shunt resistance 16 is bridged across the circuit to control the volume ofthe alternating current'impressed upon the line L the 'en erator G,

which generator is assumed to rave a com paratlvely high impedance. By arranging the potentiometer 11 and the shunt resistance 16 so that they are controlled together by the same adjusting operation, a change in the potentiometer 11 will produce a corresponding change in the volume of the current impressed upon the lineL from the source G. This will result in a corresponding change in the attraction of the core 15 by the solenoid 14, thereby producing a setting of the potentiometer 13 which will just compensate for the change in the setting of the potentiometer 11. Thus, whenever the transmission from the main transmission circuit L is made weaker, thealternating current over the control circuit is made Weaker, and vice versa. The alternating current over the control circuit, by controlling the magnetic arrangement 14-15 at the distant end, will automatically adjust the potentiometer 13 accordingly, with the result that whenever the volume at the sending station is increased or reduced a certain amount by changing the setting of the potentiometer 11, the volume impressed by the line L upon the loud speakers LS will be varied by the same amount but in the opposite direction.

The operation of the circuit may be more clearly understood from a consideration of the transmission level diagrams of Fig. 2. It will be noted from the curves of Fig. 2 that the volume supplied by the microphone M is assumed to vary from the maximum value of -43 transmission units to a 1ninimum value of -55 transmission units, therange being 50 transmission units corresponding to a ratio of strong to Weak power of approximately 100,000. Such a range of volume is frequently. produced by a transmitter picking up a high grade musical performance and the range may be even greater in'certa'in cases. It is also assumed in Fig. 2 that the maximum range of volume which can be handled by the transmission line L is 20 transmission units corresponding to a ratio of strong to weak power of only.

about 100.

In order to fully understand the transmission level diagram of Fig. 2, it will be necessary to define what is meant by a transmission unit. Let us-suppose we have a transmission circuit upon which is impressed a given power and that we measure the power received at the other end of the transmission circuit. The ratio of the power applied to the power received is the power ratio and may be expressed as R. If there is no transmission loss in the circuit, the power received will be equal to -that applied, so that the power ratio R will be unity. If the power received only h ofthat applied,the power ratio R is 1/100.

power which would besupplied by an ordi- I power may formula will be zero.

'is 1 100, t

nary telephone transmitter when spoken into by an ordinary person speaking in an ordinary tone of voice. This power may be arbitrarily taken to represent the zero transmission level. Any greater ower than this ma be represented in terms of a certain num er of positive transmiss on units, and v ce versa,any' power less than this may be represented "by a certain number of negative transmission units.

It 1s also evident that the loss in trans mission heretofore expressed in terms of the It is now evident that if there is no trans-' mission loss in' passing through the circuit, and the standard power heretofore referred to is impressed upon this circuit, the power ratio R will be unity and the loss in transmission units as calculated by the above Similarly, if there is a loss intransmission sufiiciently great so 'that only 1/100 of the power is supplied at end, so that the power ratio R is loss may be expressed in transmission units from the above formula as 20. Likewise, if, due to the use of amplifiers or for any other reason the power the receiving arriving atthe receiving point is'increased 100 times, so that the power ratio R is 100,

Y this gain may be ex ressed initransmission it units as +20. In ing' table may be computed:

'lU. Power ratio R;

Returning now to the assumed conditions of Fig. 2 with the repeater R supplying a I maximum volume of +10 transmission unlts and a' minimum of '40 transmission units,

so that the'total range 'is 50, will be seen that the correspondingpower ratios are 1/ 10,000 and 10, so that the actual ratio be-" [again the actual ratio'for this power range tween the maximum and minimumyolume is 100,000. Now letus consider what happens to the energy as it is transmittedfrom ,station A to station B. The maximum power goneratediby the transmitter of ,5 transmission units is amplified by the repeater R and raised to a tlfiDSIIliSSlOIl level of 10 is manner the follow transmission units as indi'cated'bythe heavy line curve of Fig. 2.. Up n arriving at'the volume controllin element 10, the potentiometer 11 is'ad usted in the case of the maximum powerso as to reduce it in vol ume 1 5'transmission units,fthusbringin'g it down to the level oi -'5"transmission-units. The power is now attenuatedin being trans n'iittedoverthe line section'to the next repeater' R- so. that it drops'- (loivn 'to' -25 transmission units, is then amplifiedto a level of +5 units, is'again attenuated in being transmitted over' thenext section, drop-- ping down 'to +15 units, and is amplified to a transmission level of +10 transmission units, etc.,. finally arriving at' the terminals 17 of Fig. 1 at a transmission level of- 5 transmission units.

' Similarly, the minimum Volume generated by the transmitter M of -55' units is likewise a'mplifiedby the first repeater R to bring its valueup 15 transmission units, so

that it arrives'fat a transmission level of e -40 transmission units. In this case the volume control device 10 is so' adjusted by means ofthe potentiometer 11 as to intro- 7 duce a gain in transmission, thus stepping .the volume up 15 unitsto a levelof 25.

The power is then impressed upon the transmlssion circuit and is attenuated 1n; the line section extending to the repeater R so that it fallsto a levelof -45 transmission units, being amplified by the repeater R to bring it up to'a level of 15[units, etc., the

' energy finally arriving at the terminals 17 with a power such that it reaches a transmission level of"25 units. Y i

It will be seen by comparing the two curves that at all points between the input terminals 18 of the transmission line and the output terminals 17 of'said transmission line, the maximum andminimum values will be separated by a range of just 20 transmission units, corresponding to the ratio of maximum to minimum volumeof 100. "For example, the maximum volume, upon leaving the repeater R is just +10'transmission units, while the minimum volumeis -10 transmission units. Referring to the table,

it will be seen that these two volumes correspond to power ratios of 10 and ,1/10, respectively, so that their actual ratio is 100. Similarly, the maximum and minimum values, upon arriving at the input of the repeater R are a'maximum of "20 and a minimum of 40ftransmission units. Again referring to the table, these correspond to power ratios of 1/100 and 1/10,000 so that of 20 transmission units is As hasalready been stated, the maximum volume which the line will transmit is dein thetransmission circuit, it being necessary to maintain the volume of the signal relatively greater than the noise at any given point 1n order that the signal will be heard w thout undue disturbance from the noise. In order to determine what are the maximum and minimum volumes that may be impressed upon the line L, for example.

ceiver 20 will observe that the received sig-' 11211 is distorted due to overloading the tubes at some repeater point. As soon as this condition is observed, itwill be at once known that the maximum limit of volumehas been applied to the transmission line. .If the volume indicator 19 is graduated to read in transmission units, this will be found to correspond for the case assumed to a transmission level at terminals 18 of -5 trans mission units. It also happens in the case assumed that at the point 17 the corresponding volume received would be 5,transmission units if measured with a volume indicator.

If the circuit be now tested by reducing the volume applied to the terminals 18, bearing in mind that noise is being picked up along the line L at various points, the volume will finally be reduced to a point where its ratio to the noise arriving in the receiver 20 will be so small that the noise produces a disturbing effect and tends to diswhich may be impressed upon the line .is at once known and if measured by the volume indicator 19 Wlll be found to be transmission units. The correspondmg volume arriving at terminals 17, if measured by a volume indicator, will also in the assumed case be found to be 25 transmission units.

In the operation of the system, the range of volume to be'applied to the line must, therefore, always be kept within the limits of 5 and 25 transmission units. The potentiometer 11 will, therefore,be operated preferably during pauses in the musical sel'ectionso as to cause a loss by meansof the volume control device 10 when the volume is strong, and so as to produce a gain when the volume is weak, thereby reducing the units, it willbe reduced by means of. the controlling device 10 to 5 transmission units and will arrive at the terminal 17 with a volume of ,5 transmissionfunits. Ifan instant later the volume supplied by the repeater B should drop to 40 transmission units, the controlling device would be adjusted to produce a gain of 1 5 transmission units, bringing the volume up to -25 so that the volume arriving at the terminal 17 will be 25 transmission units,

It will at .once .be seen that while the original ratio between the volume generated at the two instants under consideration by the microphone H was 100,000, the ratio between the corresponding energies received is only,100. The controlling device 12, how'- ever, will be automatically"operated over the auxiliary circuit L to introduce a gain of 15 transmission units in the one case and,

a loss of 15 transmission units inthe other case, sothat the volume for the maximum case is +10 transmission units and the volume for the minimum case is reduced to 40 transmission units. The total difference in range is units, corresponding to a ratio of 100,000, so that therelation between the maximum and minimum volumes as applied to the loud speakers will be, the

same as that generated by themicrophone,

notwithstanding that the ratio was changed during transmission over the line L. a.

While for the simplicity of illustration the controlling circuit L" has beenvillustrated as a separate circuit, it. will be apparent that if the frequency transmitted by the generator G is outside of the frequency range for which the circuit L is employed in signaling, the circuit L may be employed for transmitting the controlling current from the generator G as in carrier transmission without in any -way interfering with the transmission of the signals, suitable filters being provided, of course, to separate the controlling and the signaling currents.

It will be obvious that the general principles herein disclosed may be embodied in many other organizations widely different from those illustrated without departing from the spirit and scope of the aprange of energy volumeover a transmitting medium capable of transmitting only a narrow range ,of energy volume which consists in generating energy varying in volume over a range wider than the volume range of a transmitting medium, producing a change in the volume of the energy to be'applied to the medium when the energy volume exceeds the limits of the transmitting medium, transmitting the energy over, the medium with variations in volume extendingover a narrower range than that of the energy originally generated, receiving the energy thus transmitted over the medium, and producing a compensating change inthe volume of the received energy.

2. The method of transmitting a wide range of. energy volume over a transmitting medium capable of transmitting only a narrow range of energy volume, which consists in reducing the volume of the energy to be applied to the medium when thevolume of energy to be so applied is greater than the medium will carry, receiving the energy thus transmitted over the medium, and producing a compensating increase in the volume of the received energy.

3. The method of transmitting a wide range of energy volume over atransmitting medium capable of transmitting only anarrow range of energy volume, which consists in generating energy varying in volume over. a range wider than the volume range of a transmitting medium, increasing the volume of the energy to be applied to the transmitting medium when the volume of said energy is less than the lowest energy volume which the medium will transmit efiioiently, transmitting the energy over the medium with 'ariations in volume extending over a narrower range than that of the energy originally generated, receiving the energy thus transmitted, and producing a compensating decrease in the volume of the re ceived energy.

4. In a signaling system, a transmission medium capable of transmitting a relatively narrow range of energy volume, means to \generate signaling energy having variations of energy volume extending over a range greater than that which the medium is capable of transmitting, means for changing the volume of the energy generated when it exceeds the limits of the transmitting medium so as to bring it within the energy volume range which the medium will transmit, transmitting the energy over the medium with variations in volume extending over a narrower range than that of the energy originally generated and means at the receiving station for producing a com pensating change in the volume of the received energy in the opposite direction.

5. In a signaling system, a transmission medium capable of transmittinga relatively narrow range of energy volume, means to generate signaling energy having variations of energy volume extending over a range greater than that which the medium is capable of transmitting. means for decreasing the volume of the generated energy when it exceeds the highest energy volume which the transmitting medium will carry, and means for producing a' compensating increase in the received energy.

6. In a signaling system, a transmission medium capable of transmitting a relatively narrow range of energy volume. means to generate signaling energy ha ving variations of energy volume extending over a range greater than that which the medium is capable of transmitting, means for increasing the volume of the generated-energy when it falls below the lowest energy volume which the transmitting medium will carry, transmitting the energy over the medium with variations in volume extending over a narrower range than-that of the energy originally generated and means forproducingv a compensating decrease in the received energy. r 1

7. Ina signaling system, a transmission medium capable of transmitting a relatively narrow range of energy volume, meansito generate signaling energy having variations of energy volume extending over a range greater than that which the medium is bapable of transmitting, means for chan 'ng" the volume of the generated energy when it exceeds the energy volume limits which the transmitting medium will carry, and means for automatically producing a-compensating change in the received energy in the opposite direction. I

8. In a signaling system, a transmission medium capable of transmitting a relatively narrow range of energy volume, means to generate signaling energy having variations of energy volume extending over a range greater than that which the medium is ca pable of transmitting, means for increasing the volume of the generated energywhen it falls below the lowest energy volume which the transmitting medium will carry, and means for automaticallyproducing a compensating decrease in the received energy.

9. In a signaling system, a transmission medium capable of transmitting a relatively narrow range of energy volume, means to generate signaling energy having variations of energy volume extending over a range greater than that which the medium is capable of transmitting, means for decreasing the volume of the generated energy when it exceeds the highest energy volume whichthe transmitting medium will carry, and means for automatically producing a compensating increase in the received energy.

1.0. In a signaling system, a transmittin medium only capable of transmitting a re atively narrow range of energy volume, means for generating signaling ener varying in energy volume over a wi er range than that which the transmitting medium will carry, means for generating controlling energy of constant volume, means to change the volume of said variable signaling energy before. applying it tosaid medium when it exceeds the limits of the range which themedium wiil transmit, means to simultaneously produce a corresponding change in the volume of range than that which the transmitting medium will carry, means for generating controlling energy of'constant volume, means to decrease the volume of. said variable signaling energy before applying it to the medium when it exceeds the maximum value which the transmittingmedium will carry, means to produce a simultaneous.

and corresponding change in the volume of said controlling energy, means to transmit said controlling energy to a receiving station, means at the receiving station to receive the signaling energy, and means at said station responsive to the change in the volume of said controlling energy to pro duce a compensating increase in the received signaling energy.

12. In a signaling system, a transmitting medium only capable of transmitting a relatively narrow range of energy volume, means for generating signaling energy varying in energy volume over a wider range than that which the transmitting medium will carry, means for generating controlling energy of constant volume, means to increase the volume of said variable signaling energy before applying it to the medium when it falls below the minimum value which the transmitting medium will carry, means. to produce a simultaneous and corresponding change in the volume of said controlling energy, means to transmit said controlling energy to a receiving station, means at the receiving station to receive the signaling energy, and means at said station responsive to the change in the volume of said controlling energy to 'pro duce a compensating decrease in the received signaling energy.

13. The method of transmission control comprising reducing all levels of energy input in a system to levels below a given maximum. transmitting energy at the reduced level, and reproducing at a receiving point energies of difi'erent levels in substantial accordance with the unreduced original energy.

14. The method of transmission control of produced energies extending over a wide range of levels comprising transmitting energy only below a given level less than the maximum of said produced levels, transmitting control current variations, and reproducing energies under-control of said variations extending over a range of levels of substantially the same width as the original level.

15. The method of efiectively transmitting energy varying through a wide range of volume over a system of limited volume range capacity which consists in making changes at one point in the systemtobring the energy variations within the volume limitsof the system transmitting the energy over the medium with-variations in volume extending overa narrower range than that of the energy originally generated and making opposite changes at another point in the system for compensation.

16. The method of effectively transmitting energy varying through a wide range of volumes over a system of limited volume range capacity which comprises changing the loss characteristics at the input of the system of limited capacity to bring the input energy within the limits of the system transmitting the energy over the medium with variations in volume extending over a narrower range than that of the energy originally generated andchanging the loss characteristics at the output of the system to compensate for the changes made at the input of the system.

17. The method of effectively transmitting energy of a wide range of volumes of energy over a system of limited volume range capacity which comprises varying the energy level at the input of the system to bring the input energy within the volume limits of the system, transmitting to the output end of the system current variations representing the magnitude and direction of the changes in energy level at the input end and utilizingthe transmitted current variations at the output end of the system to eflt'ect changes in the level of the energy received from the system corresponding in ma nitude but opposite in effect.

18. The method of effectivelytransmit ting energy of a wide range of volumes of energy over a system of limited volume range capacity which comprises varying the energy level at the input of the system of limited ran cc to bring the input energy within the volume limits of the system. transmitting to the output of the svstem current variations corresponding to changes in the energy level at the input and varying the energy level at the output of the system in accordance with the transmitted current variations.

1!). In a wave transmission system, a source of energy varying through a wide range of volume. a transmission circuit of limited volume range capacity supplied with said energy, means for reducing the volume range of the energy input to said circuit and means for transmitting the output end of the system current variations corresponding to the changes in level of the input energy.

20. In a wave transmission system, a source of energy varying through a wide range of volumes, a circuit of limited volume range capacity supplied with said energy, means for changing the volume range of the energy input to said circuit, and means for producing corresponding changes in the energy. output of said circuit, in the opposite direction from the energy input changes.

21. In a transmission system, sources to produce energy of various levels to be transmitted, a transmission circuit, means for reducing the level of energy from said sources to less than a given maximum and for applying energy of the reduced level to'said circuit, means controlled by the energy reducing means for transmitting control current variations and means at a receiving point actuated in accordance with said control current variations for reproducing from the energy of reduced level energies of various levels corresponding to the energies from said sources.

22. In a wave transmission system, a source of energy of a wide range of volumes, a circuit of limited volume range capacity supplied with said energy, means for varying the energy input to said circuit to bring it within the volume limits of said circuit, means for transmitting indications of the the volume limits of said first-mentioned circuit-and for transmitting signals corresponding in direction to said input energy adjustment for adjusting the energy output of said first-mentioned circuit in the o posite direction from said input energy ad ustment.

24. In a signaling system having transmitting and receiving stations, meansfor changing the energy input delivered to said transmitting station, means for transmitting signals to said receiving station indicating the magnitude and direction of such chan es in said energy input, and means control ed by said signals for changing the energy o,ut put of said receiving station to comp," sate for said changes in said energy input-2t said transmitting station.

In testimony whereof, I have signed my name to this specification this 18thddy of June 1924.

ALVA B. CLARK. 

